Decorative sheets using paper and resin sheet, or decorative materials such as decorative material in the form of plate, in which the above-mentioned decorative sheet is adhered to an adhered base material, are used in various uses such as construction interior and exterior materials. These decorative sheets and decorative materials, in general, are often required to have surface strength such as scratch resistance and the like. For the above-mentioned reasons, for example, (1) ones, in which a curing resin layer of two-component curing resin, ionizing radiation curing resin, or the like is formed as an even thickness resin coated membrane (Japanese Patent Application Laid-Open (JP-A) No. 53-64289), is conventionally used for the surface of the decorative sheet. Comparing to two-component urethane resins and the like, such ionizing radiation curing resin has various advantages such as: excellent in productivity because instant curing is possible; solvent drying is not necessary and can be piled up; and further as result, relief printing in a pattern is possible.
Further, a decorative sheet, whose curing resin layer of the surface is formed into a convex-concave pattern, is proposed in the purpose of a convex-concave surface design, improving abrasion resistance or the like. For example, (2) a decorative sheet 20 having a configuration shown in cross-sectional view in FIG. 4, that on a pattern printed layer 22 provided on a base material 21, coating film layer 23 of an urethane based resin ink is provided on the entire surface, and further thereon, a convex-concave pattern 24 formed by the relief printing of the urethane base resin ink is provided (JP-A No. 8-100397). Or (3) a decorative sheet 20 having a configuration shown in cross-sectional view in FIG. 5, that on a pattern printed layer 22 provided on a base material 21, coating film layer 23 of an urethane based resin ink is provided on the entire surface, a convex-concave pattern 24 formed by the relief printing of the urethane base resin ink is provided thereon, and further on the entire surface of the convex-concave pattern 24, an overcoat layer 25 of a curing resin is provided (JP-A No. 8-244193).
On the other hand, various design expression is possible in forming of surface resin layers such as curing resin layer, using a doctor blade and a gravure plate (gravure coating, gravure printing), by adjusting a cell volume in order to make variation in thickness of the resin layer, or by forming in a pattern.
In the above-mentioned gravure coating or gravure printing, doctor streak may occur in long time operation. The doctor streak occurs when a tip of the doctor blade is chipped off, a groove shaped damage (doctor damage) occurs across the tip, so that the ink of this part is not scraped off sufficiently, because the doctor blade is not worn evenly in its width direction. Such doctor streak can be avoided if the doctor blade is changed earlier, or can be improved by using a steel doctor coated with ceramic (hereinafter, referred to as “ceramic doctor” for short) as the doctor blade instead of a conventional steel doctor blade.
The improvement of the doctor streak is attempted also in an aspect of compositions of the ink or coating liquid. For example, compositions containing an inorganic pigment (special light calcium carbonate) having rosette crystal (JP-A No. 5-51549), containing an amine salt of N-benzoyl amino alkane acid in an aqueous ink (JP-A No. 6-220385), or containing spherical filler such as a polycarbonate based resin and the like (JP-A No. 11-277685 (paragraph 0013)) are proposed.
However, particularly when the ink or coating liquid contain delustering agent such as delustering silica, the doctor streak is likely to occur. The delustering silica is used when a delustered surface (including a low-luster surface in addition to a delustered surface, as it is named) is required, for example, when luster on a surface of a decorative material is not wanted. Therefore, the resin layer on the surface is formed as a luster adjusting resin layer in which the delustering agent is added (Japanese Patent No. 2856862). Though there are various types of delustering agent, the delustering silica is most common in view of high delustering effect and low cost.
In the decorative sheet such as above-mentioned (1), in which a curing resin layer of an even thickness is formed by coating on the entire surface, abrasion resistance is improved by the curing resin layer. However, a problem of grain depression is likely to occur. The grain depression is a phenomenon that convex-concave, such as conduit or the like of the adhered base material surface, stands out on the surface of the decorative sheet when the decorative sheet is adhered to an adhered base material such as wooden substrate, such as a lauan plywood, a particle board and the like, to form a decorative material. Particularly, the phenomenon occurs when the decorative sheet is in a form of a decorative paper, a coated paper or the like, and the base material sheet is thin like a paper.
It was found that, in the decorative sheet provided with a convex-concave pattern by relief printing as the above-mentioned (2) and (3), not only the expression of the three-dimensional design, the grain depression can be made not visible by the convex-concave pattern, and further, scratch resistance can also be obtained. However, on the lower side of the convex-concave pattern 24 of the decorative sheet of (2), the coating film layer 23, of the curing resin, as same as the convex-concave pattern is provided. On the upper side of the convex-concave pattern 24 of the decorative sheet (3), the overcoat layer 25, of the curing resin, as same as the convex-concave pattern is provided. Therefore, the coating process of the coating film layer or the overcoat layer is necessary in addition to the relief printing of the convex-concave pattern so that high cost in processing and high material cost are inevitable.
In the viewpoint of the cost, a configuration of base material 21/pattern printed layer 22/convex-concave pattern 24, omitting the coating film layer or the overcoat layer, can be presented. However, with such configuration, sufficient property cannot be obtained in applications in which scratch resistance or contamination resistance is required. This is because, even though contamination resistance can be imparted to a convex part “a” of the convex-concave pattern 24 by forming the convex-concave pattern with curing resin, the lower layer of the convex-concave pattern, such as the pattern printed layer 22 or base material sheet 21, is bared in a concave part “b” of the convex-concave pattern in the relief printing. Therefore, contamination resistance of the decorative sheet is deteriorated as a whole, due to the poor contamination resistance of the lower layer (refer to FIG. 4).
On the other hand, when the delustering silica is added in order to adjust the luster of the surface, there is a problem that the doctor streak tends to occur. The tendency is apparent particularly when the curing resin layer on the surface is formed of the ionizing radiation curing resin, especially with no solvent. Further, in case of using the ionizing radiation curing resin by itself, the surface thereof tends to have a strong luster and it is difficult to weaken the luster. Therefore, the delustering agent must be added in the applications in which the strong luster is not wanted, so that improvement of the doctor streak and making the manufacturing easier are inevitable problems.
A reason that the addition of the delustering agent, when the resin is the ionizing radiation curing resin, has tendency to lead to the doctor streak is as follows. When a two-component curing type urethane resin and the like is diluted with a solvent and used, a lift up effect, wherein the delustering agent float up to the surface in volume shrinking of the coating film due to drying of the solvent, will contribute to the delustering. However, when no solvent is used, an adding amount or a particle diameter of the delustering agent is needed to be increased since there is no lift up effect. Moreover, when no solvent is used, a leveling effect after the coating is low so that the doctor streak tends to remain, being another reason. Although the doctor streak is improved by the use of the ceramic doctor, a difference by adding the delustering silica still remains.